Lubricating oils



' spindle to the heaviestlubricating oils.

Patented Apr. 11, 1939 UNITED STATES LUBRICATING OILS Raphael Rosen, Cranford, and Robert M. Thomas, Elizabeth, N. J., assignors to Standard Oil Development Company, a corporation of Delaware No Drawing. Application November 10, 1933, Serial No. 697,470

2 Claims. (Cl. 87-9) A The present invention relates to improved lubricating oils and methods for producing them, and particularly to oils of low oxidation rate and low sludging tendency. The invention will be fully understood from the following description:

It has long been observed that well refined oils show a higher rate of oxidation than the unrefined oils from which they are obtained. This has been attributed to the fact that refining methods remove certain materials whichinhibit oxidation and this apprehension seems to be plausible because inhibiting substances are known which can be added to oils to greatly reduce their oxidation rates. Among the known inhibitors are phenolic substances such as the cresols, naphthols and anthrols. For some purposes these materials serve excellently. However, it has been found that the addition of these materials always tends to increase the sludging tendency of the oil, for example, as measured by the Sligh test, see Proceedings of the American Society for Testing Materials, 24, 984, II (1924) A new class of inhibitors has now been discovered which are not only much more powerful than the phenolic inhibitors, but which actually reduce the sludging tendency of the oils. These materials comprise certain sulfur compounds specifically aliphatic and aromatic polysulphides and the corresponding polyselenides and polytellurides. By the term polysulfide we intend to include only substances of the following general formula SSSz R This does not include, however, the well known disulphides of the general formula In each of the above formulae the R+R' denotes alkyl or aryl groups. The a; may represent 1 or more sulphur atoms. This is preferably under 3 since the penta and higher sulphides are corrosive while those below 3 are not.

The present inhibitors can be used in any type of well refined hydrocarbon oils from the light They are most desirable, however, when used in oils of a strongly parafiinic nature such as those derived from pa'raffin base crudes, or from oils which have been extracted with agents of the type of phenol, cresol, sulfur dioxide, nitrobenzol and dichlorethyl ether, all of which have the property of removing the non-paraffinic constituents. These inhibitors are also well suited to oils prepared by hydrogenation or destructive hydrogenation, and to oils refined'by vigorous action with concentrated and even fuming sulfuric acid; in

other words, the so-called white mineral oils. They are likewise useful in waxes and in the synthetic oils prepared by chemical or electrical condensation.

While essentially parafflnlc oils described above are the most important ones, it is worth noting that the present inhibitors are also effective in reducing the oxidation rate of naphthenic or sisphaltic oils which have been well refined. This is a most unusual and unexpected property and may be taken as an indication that these inhibitors are different in their action from those for merly used, namely, the phenolic, because these latter show no appreciable reduction of the oxidation rate of naphthenic oils, whereas, the present agents show a very substantial reduction.

The present inhibitors may be used in relatively small amounts, say as low as .01% for highly refined oils such as white oils or less refined oils in the lower range of temperatures, say below 150 C. but usually they are preferred in somewhat larger amounts for example, .05 to 0.1% and as much as 1% can be used at higher temperatures although this is not necessary and is usually undesirable. They may be addeddirectly to the finished lubricating oil in any desired form for example, directly or in a suitable solvent, such as carbon disulfide or carbon tetrachloride or the like, and then incorporated with the oil. The solvent may be removed by distillation with steam, or under vacuum.

It is preferred to add pure agents but oils known to contain these materials may be added to the refined oils so as to incorporate the desired quantitles of the inhibitors. It should also be understood that the sulfur compounds should be added after all of the refining steps have been completed because the usual refining methods will remove sulfur compounds and their equivalent. It will be understood, of course, that if the type of refinement is such as not to accomplish the removal of sulfur, then the agents may be added prior to such treatment.

Most of the above mentioned substances are of the type known as corrosive in that they tarnish copper and brass but it has been determined that this is of little consequence, especially where engines are run at elevated temperatures, for example aeroplane engines, but some of the substances are not corrosive. These latter are, there fore, preferable. They can be made by reaction of unsaturated hydrocarbons and sulfur or sulfur chloride or the corresponding selenium and tellurium compounds. Cracked oils, for example, cracked wax may be used to produce good noncorrosive substances, or fatty acid containing unsaturated group such as lard 011. Another method of producing polysulphide is by treatment of a mercaptan with sodium plumbite adding enough sulphur to make the desired polysulphide.

The folio plea are given to e the use of the present inhibitors and the prop ertiee oi the inhibited oils: 1

Example I Blank +0. 1% Time intervals Blank butyl pentesulphid v f l This materiel was conceive and did not exert its effect as long as might be desired.

Example If The blank used in this experiment was a. well refined motor oil 8. A. E. Grnde 50. The polysulphid inhibitorwns produced by reectlng wax fractions (boiling 2% to 6%" F.) at 150 to 200 C.'with 10% S2C12.- The product contained 2 /2% sulfur and a small amount of chlorine which. was removed by treatment with alcoholic soda. The tests were conducted as in the prior example.

Time intervals Blank 1% g fg g 1 132- 22 2 11s 20 a s2 22 4 i9 20 hocmnle Ill 'lotllez-zeuneblcnlicausedinllxample Han inhibitor is added prepared by cooking lard oil at 1st to 200 C. with, approximately, 10% sulphur. The tests were conducted as before.

Time mw- 0.1 lnhib- 0.257 inhibval Blank I Kim him:

. 15 With the present bitor .1% LS too small to be eflective tor the entire test at the high tempera,- tin-e used but its influence is clearly perceptible. At lower temperatures this amount is sumcient but at 209 C. it is preferable to use 25% which is altogether'satisiectory.

The present invention is not to be limited by any theory of inhibitor action nor to any particular inhibitors nor to any particular oils containing them, but only to the following claims in which it is desired to claim all novelty inherent in the invention.

We claim:

1. An improved oil composition resistant to deterioration at elevated temperatures of the order encountered in an internal combustion engine comprising a. viscous hydrocarbon lubricating oil and less than 1% cl an organic polysulfide prepared by reaction of a. mercaptan with sodium plumbite and sulfur, the latter being suflicient to produce a. polysulflde containing more than two sulfur atoms to the molecule.

2. An improved lubricating composition resistant to deterioration at elevated temperatures of the order encountered in an internal combustion engine comprising a. viscous hydrocarbon lubrieating oil and less than 2% oi butyl pentasmfide.

RAPHAEL ROSEN. ROBERT M. THOMAS. 

